samurai_k

A few years ago I ordered the solid inners from FVD as I already had the RS outers.

Here are the fvd part numbers that were on my order

993 347 031 81AXG
8708.94.90
Axial joint for tie rod 993 RS / RSR / GT2

MarinS4

Hey Bill, I am curious as to why you’d recommend the thin solid subframe bushings starting at RSR height and lower? Not trying to challenge you but understand the logic behind the recommendation.

When I did Rennline Solid Subframe bushings (old version) they shoved the subframe almost 10mm higher in chassis. At RS ride height they helped achieve ideal camber settings (when lowered some 993’s struggle with excess camber). I understand as the multi link rear gets lower you enter a more aggressive camber arc. This could be a good thing or perhaps not?

By raising the subframe you raise the roll center. It’s what you want to do when lowering a car. I have to believe this also helps maintain proper roll coupling front to rear when combined with RS wheel carriers. If I recall correctly the RS wheel carriers (one of my favorite mods) dropped the ball joint 26mm vs stock.

Bill Verburg

the thin side mounts do the same thing as the short RS wheel carrier steering arm, they correct geometry on a lowered car. The geometry they correct induces additional unwanted toe from suspension travel

Here's what's happening at the front, the black axis is for a stock RoW 993, the blue axis shows where an uncorrected 993RS height car would be and the red axis shows where an uncorrected US993 would be, the keep in mind that the ideal toe curve is a vertical line, the worst curve is a horizontal line.. W/ stock uprights the US 993 is best, what the RS wheel carriers do is move the x axis down by ~20mm, All of these w/ either wheel carrier is pretty acceptable some are just more so

Hee are the same sorts of curves for the back, being more vertical than the front these are better and benefit less from correction, on a lowered car the thin rear sides move the axis down by the delta from stock

ToSi

^^Somethings not right with those toe curves.

The trailing arm 911's should have approximately linear toe curves while the rear toe curve for the 993 resembles a C shape. At stock ride height, the suspension is roughly in the middle of the curve, e.g. ->C such that movement up or down results in stabilizing toe-in.

Lowering the car a bunch moves the suspension away from the middle and to the part of the curve where toe increases in compression but _decreases_ in rebound. At RS ride height, this can be countered by slightly increased toe-in such that the total toe stays positive as the suspension moves through its total range. (doesn't need to be said but toe out is a bad thing in the rear of a 911)

Raising the subframe resets the rear suspension to operate closer to the middle of the C-shaped curve along with nudging the roll center upward..

boomboomthump

OK, everything is on order with the exception of the drop links for the RS sway bars.


I believe my only options here are Tarett, Elephant or stock RS (haven't found any others). The Elephant ones look nice but given the comments above around the glued on seals (and them potentially falling off?), the Tarett links are likely the way to go here from what I see? There's not really any price difference between them and the OEM RS but the Tarett links provide adjustability to dial out any pre-load while at static ride height.

Assuming the crowd here is in-line with my thought process, will pull the trigger on the Tarett links.

ToSi

Unless the car has had a really rough life, there shouldn't be enough preload due to side-to-side ride height difference to really matter. Stock links are well sealed and will last a decade or two, unsealed monoballs' lifespan will depend on what they're exposed to. I've had some that sound like a taxicab after a few years. Either should be fine for a nice weather driver.

MB965

Agree Tarret and RS are good choices, I have used both. On a street driven car the adjustables are not "needed", but if they cost the same why not. The RS will have a longer service life and no noise.
The Tarret links I used in the rear had to be shortened to be optimized for my components.

Also the factory new RS rear stabilizer bar I got, did not fit the factory rubber bushings all that good. The bends in the bar are complex and were off bit. I had to grind out the ID of the bushing a bit to keep it from binding.
Hopefully you won't encounter that issue.

boomboomthump

OK, perhaps I shouldn't overthink this. Leaning towards the RS drop links now.


Mike, I haven't ordered the rear RS sway bar just yet. Will do so in the coming weeks when I'm closer to getting the motor back in. I ordered the front for now so I can get everything in the front of the car squared away. While I'm at it, just picked up a reseal kit for the steering rack. This is as good a time as any to do that job too.

Coleman

Did you check out those BBI tie rods? They look really nice.. I'm sort of on the fence with BBI tho.. They make some nice kit, but had some attitude in email exchanges .. Definitely part of the "new modification vendor school" -

Coleman

If you're looking for some still, I have some good condition original rear RS Drop links (curved for RS sways) 993 333 073 82 PM me- they wouldn't work with the KW3's (not long enough for the mount point on the lower shock body) and I had to purchase something else, I went with the Elephants, (the ones with all the glue all over.. )

boomboomthump

Crap, I didn't realize that. I'm running KW V3's as well.

I haven't ordered the rear RS sway bar or drop links, only the front. Will have to go with adjustable aftermarket drop links in that case. Had I known though, I probably would have opted for matching drop links for the front instead of OEM RS. Oh well.



Also, yes, I had seen the BBI outers. Didn't see a compelling reason to pay such a premium over the OEM RS.

boomboomthump

Edit... oops. Meant to post in my build thread.

MarinS4

I appreciate the graphs Bill, as always you've proven to possess an amazing amount of information that's not readily available.

I drew the red line to better visualize where the two knee points are. Assuming zero wheel travel is ROW height I can see how a lowered car would enter the aggressive part (40mm+) of toe curve at full bump.

I believe RS is 20mm lower in the rear than ROW. That means there's only 20mm of travel left in sweet spot before entering the aggressive part of toe curve.

I'd want to setup my car to live right in that center area as much as possible. That way during cornering and subsequent body roll, toe gains and losses would be equal and offset each other.

Thanks again Bill, it was all of your shares such as these in the archives that led me down the path of doing RS carriers, bushings and subframe upgrades.

boomboomthump

I've been plugging away at all my upgrades over the last last few weeks. Which has also led to other rabbit hole items like all new wheel bearings, etc (soooo glad I did, btw).


Have a general question/observation for the suspension gurus to educate me on...

As I was pulling the rear suspension all apart (removed the entire subframe), I disconnected the camber and KT arms at the rear wheel carrier first, leaving the bushing end connected to the subframe. I saw first hand the effects of the pre-loaded bushings while those ends of the arms were still torqued to spec in the ride height position. You can take the free end of the arm and flex it up or down and release which results in *boing!* ...it springs back into position.

So based on that, how much do control arms with bushings play an effect on compression/rebound overall? Is it negligible since the weight of the car/motor is obviously a lot more than my simulation above?

The reason I'm curious is that since I'm swapping to RS style "sport" bushings, which are firmer and exhibit less slop/play side to side, I presume the firmness also increases both the "compression" resistance and "rebound" these "sport"-bushed arms add to the overall suspension? Perhaps negligible but the reason I'm truly curious about this is that, if you were to switch full mono-ball arms everywhere (which obviously do not spring back into position like mono-*****), is there any noticeable loss of compression/rebound in the overall system, which then needs to be accounted for in the valving/spring rates when transitioning from bushed control arms to full mono-***** in full on track setups?


Just curious here but seems like a reasonable assumption considering bushed arms need to be torqued down in ride height position and have some spring/rebound to them. Conversely full mono-***** are completely free flowing and remove any spring/rebound from the arms.

Tlaloc75

I noticed the same and assumed that the effect was negligible. It's only a few pounds of force, so it's a very small percentage of the total system.